Collaborative study brings new insights into 'Livestock Associated' MRSA in US pigs

Peter Davies, Ph.D., professor in the University of Minnesota College of Veterinary Medicine, in partnership with scientists from the USDA National Animal Disease Center and the Iowa State University College of Veterinary Medicine, conducted two studies that found Methicillin-resistant Staphylococcus aureus (MRSA) appears to be much less common in US pig herds than anticipated, but more varied than in pigs in Europe. The studies also found that both the main European variety of MRSA and another variety that has up to now only been seen in North America showed little genetic capability to cause infections in humans.

The first study looked at this North American variant of MRSA found in Iowa swine and in veterinarians in several states. The team found that MRSA bacteria appeared to have diminished capability to cause human disease compared with similar variants that caused disease in the human population. When MRSA adapts to the pig, it seems to lose some of the material necessary to cause infections in people.

The second study looked at the prominence of MRSA in US swine herds. Other than the control group, no herds tested positive for MRSA, suggesting that MRSA prevalence in US swine herds is no more than 10 percent. This is noticeably lower than in Europe, where some countries see an estimated 70 percent of swine herds infected.

According to Davies, "As far as we can tell, there is little or no impact on public health. No serious infections have been seen in swine workers or veterinarians."

Davies encourages more studies to be done on MRSA in relation to US swine herds and veterinarians.

"US pigs certainly have MRSA, it's just not widespread at this point," Davies said. "That doesn't mean it won't change."